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• C++ game loop example

  - by David

  Can someone write up a source for a program that just has a "game loop", which just keeps looping until you press Esc, and the program shows a basic image. Heres the source I have right now but I have to use SDL_Delay(2000); to keep the program alive for 2 seconds, during which the program is frozen. #include "SDL.h" int main(int argc, char* args[]) { SDL_Surface* hello = NULL; SDL_Surface* screen = NULL; SDL_Init(SDL_INIT_EVERYTHING); screen = SDL_SetVideoMode(640, 480, 32, SDL_SWSURFACE); hello = SDL_LoadBMP("hello.bmp"); SDL_BlitSurface(hello, NULL, screen, NULL); SDL_Flip(screen); SDL_Delay(2000); SDL_FreeSurface(hello); SDL_Quit(); return 0; } I just want the program to be open until I press Esc. I know how the loop works, I just don't know if I implement inside the main() function, or outside of it. I've tried both, and both times it failed. If you could help me out that would be great :P

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• C++ reference variable again!!!

  - by kumar_m_kiran

  Hi All, I think most would be surprised about the topic again, However I am referring to a book "C++ Common Knowledge: Essential Intermediate Programming" written by "Stephen C. Dewhurst". In the book, he quotes a particular sentence (in section under Item 5. References Are Aliases, Not Pointers), which is as below A reference is an alias for an object that already exists prior to the initialization of the reference. Once a reference is initialized to refer to a particular object, it cannot later be made to refer to a different object; a reference is bound to its initializer for its whole lifetime Can anyone please explain the context of "cannot later be made to refer to a different object" Below code works for me, #include <iostream> using namespace std; int main(int argc, char *argv[]) { int i = 100; int& ref = i; cout<<ref<<endl; int k = 2000; ref = k; cout<<ref<<endl; return 0; } Here I am referring the variable ref to both i and j variable. And the code works perfectly fine. Am I missing something? I have used SUSE10 64bit linux for testing my sample program. Thanks for your input in advance.

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• Functions and arrays

  - by Ordo

  Hello! My little program below shall take 5 numbers from the user, store them into an array of integers and use a function to print them out. Sincerly it doesn't work and nothing is printed out. I can't find a mistake, so i would be glad about any advice. Thanks. #include <stdio.h> void printarray(int intarray[], int n) { int i; for(i = 0; i < n; i ++) { printf("%d", intarray[i]); } } int main () { const int n = 5; int temp = 0; int i; int intarray [n]; char check; printf("Please type in your numbers!\n"); for(i = 0; i < n; i ++) { printf(""); scanf("%d", &temp); intarray[i] = temp; } printf("Do you want to print them out? (yes/no): "); scanf("%c", &check); if (check == 'y') printarray(intarray, n); getchar(); getchar(); getchar(); getchar(); return 0; }

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• basic file input using C

  - by user1781966

  So im working on learning how to do file I/O, but the book I'm using is terrible at teaching how to receive input from a file. Below is is their example of how to receive input from a file, but it doesn't work. I have copied it word for word, and it should loop through a list of names until it reaches the end of the file( or so they say in the book), but it doesn't. In fact if I leave the while loop in there, it doesn't print anything. #include <stdio.h> #include <conio.h> int main() { char name[10]; FILE*pRead; pRead=fopen("test.txt", "r"); if (pRead==NULL) { printf("file cannot be opened"); }else printf("contents of test.txt"); fscanf(pRead,"%s",name); while(!feof(pRead)) { printf("%s\n",name); fscanf(pRead, "%s", name); } getch(); } Even online, every beginners tutorial I see does some variation of this, but I can't seem to get it to work even a little bit.

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• "Address of" (&) an array / address of being ignored be gcc?

  - by dbarbosa

  Hi, I am a teaching assistant of a introductory programming course, and some students made this type of error: char name[20]; scanf("%s",&name); which is not surprising as they are learning... What is surprising is that, besides gcc warning, the code works (at least this part). I have been trying to understand and I wrote the following code: void foo(int *str1, int *str2) { if (str1 == str2) printf("Both pointers are the same\n"); else printf("They are not the same\n"); } int main() { int test[50]; foo(&test, test); if (&test == test) printf("Both pointers are the same\n"); else printf("They are not the same\n"); } Compiling and executing: $ gcc test.c -g test.c: In function ‘main’: test.c:12: warning: passing argument 1 of ‘foo’ from incompatible pointer type test.c:13: warning: comparison of distinct pointer types lacks a cast $ ./a.out Both pointers are the same Both pointers are the same Can anyone explain why they are not different? I suspect it is because I cannot get the address of an array (as I cannot have & &x), but in this case the code should not compile.

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• Errors not printing correctly..Is this logic flow correct? c++

  - by igor

  Example user input: PA1 9 //correct PJ1 9 //wrong, error printed "Invalid row" because it is not between A and I PA11 9 //wrong, error printer "Invalid column" because it is not between 1 and 9. The problem I am having is that it should clear the remaining input and then ask for the user to enter the "move" again, and it is not. Where did I go wrong? I've been at it for a while and still got no progress.. void clearInput() { cin.clear(); } bool getCoords(int & x, int & y) { char row; while(true){ cin>>row>>y; row=toupper(row); if(/*(id=='P' || id=='p' || id=='D' || id=='d') && */row>='A' && row<='I' && isalpha(row) && y>=1 && y<=9){ x=row-'A'; y=y-1; return true; } else if(!(y>=1 && y<=9)){ cout<<"Invalid column\n"<< endl << endl; cout<<y; clearInput(); cout<<y; //return false; } else{ cout<<"Invalid row\n"<< endl << endl; clearInput(); //cout<<x<<y; //return false; } } }

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• Can't open COM1 from application launched at startup

  - by n0rd

  I'm using WinLIRC with IR receiver connected to serial port COM1 on Windows 7 x64. WinLIRC is added to Startup folder (Start-All applications-Startup) so it starts every time I log in. Very often (but not all the time) I see initialization error messages from WinLIRC, which continue for some time (couple of minutes) if I retry initialization, and after some retries it initializes correctly and works fine. If I remove it from Startup and start manually at any other moment it starts without errors. I've downloaded WinLIRC sources and added MessageBox calls here and there so I can see what happens during initialization and found out that CreateFile call fails: if((hPort=CreateFile( settings.port,GENERIC_READ | GENERIC_WRITE, 0,0,OPEN_EXISTING,FILE_FLAG_OVERLAPPED,0))==INVALID_HANDLE_VALUE) { char buffer[256]; sprintf_s(buffer, "CreateFile(%s) failed with %d", settings.port, GetLastError()); MessageBox(NULL, buffer, "debug", MB_OK); hPort=NULL; return false; } I see message box saying "CreateFile(COM1) failed with 5", and 5 is an error code for "Access denied" error according to this link. So the question is why opening COM-port can fail with such error right after booting Windows and proceed normally few seconds or minutes later?

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• OSX launchctl programmatically as root

  - by Lukas1

  I'm trying to start samba service using launchctl from OSX app as root, but I get error status -60031. I can run without problems the command in Terminal: sudo launchctl load -F /System/Library/LaunchDaemons/com.apple.AppleFileServer.plist` In the objective-c code, I'm using (I know it's deprecated, but that really shouldn't be the issue here) AuthorizationExecuteWithPrivileges method. Here's the code: NSString *command = @"launchctl"; // Conversion of NSArray args to char** args here (not relevant part of the code) OSStatus authStatus = AuthorizationCreate(NULL, kAuthorizationEmptyEnvironment, kAuthorizationFlagDefaults, &_authRef); if (authStatus != errAuthorizationSuccess) { NSLog(@"Failed to create application authorization: %d", (int)authStatus); return; } FILE* pipe = NULL; AuthorizationFlags flags = kAuthorizationFlagDefaults; AuthorizationItem right = {kAuthorizationRightExecute, 0, NULL, 0}; AuthorizationRights rights = {1, &right}; // Call AuthorizationCopyRights to determine or extend the allowable rights. OSStatus stat = AuthorizationCopyRights(_authRef, &rights, NULL, flags, NULL); if (stat != errAuthorizationSuccess) { NSLog(@"Copy Rights Unsuccessful: %d", (int)stat); return; } OSStatus status = AuthorizationExecuteWithPrivileges(_authRef, command.UTF8String, flags, args, &pipe); if (status != errAuthorizationSuccess) { NSLog(@"Error executing command %@ with status %d", command, status); } else { // some other stuff } I have also tried using different flags then kAuthorizationFlagDefaults, but that led to either the same problem or error code -60011 - invalid flags. What am I doing wrong here, please?

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• Writing a generic function that can take a Writer as well as an OutputStream

  - by ebruchez

  I wrote a couple of functions that look like this: def myWrite(os: OutputStream) = {} def myWrite(w: Writer) = {} Now both are very similar and I thought I would try to write a single parametrized version of the function. I started with a type with the two methods that are common in the Java OutputStream and Writer: type Writable[T] = { def close() : Unit def write(cbuf: Array[T], off: Int, len: Int): Unit } One issue is that OutputStream writes Byte and Writer writes Char, so I parametrized the type with T. Then I write my function: def myWrite[T, A[T] <: Writable[T]](out: A[T]) = {} and try to use it: val w = new java.io.StringWriter() myWrite(w) Result: <console>:9: error: type mismatch; found : java.io.StringWriter required: ?A[ ?T ] Note that implicit conversions are not applicable because they are ambiguous: both method any2ArrowAssoc in object Predef of type [A](x: A)ArrowAssoc[A] and method any2Ensuring in object Predef of type [A](x: A)Ensuring[A] are possible conversion functions from java.io.StringWriter to ?A[ ?T ] myWrite(w) I tried a few other combinations of types and parameters, to no avail so far. My question is whether there is a way of achieving this at all, and if so how. (Note that the implementation of myWrite will need, internally, to know the type T that parametrizes the write() method, because it needs to create a buffer as in new ArrayT.)

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• C++ templates error: instantiated from 'void TestClass::testMethod(T, std::map) [with T = SomeClass]

  - by pureconsciousness

  Hello there, I've some problem in my code I cannot deal with: #ifndef TESTCLASS_H_ #define TESTCLASS_H_' #include <map> using namespace std; template <typename T> class TestClass { public: TestClass(){}; virtual ~TestClass(){}; void testMethod(T b,std::map<T,int> m); }; template <typename T> void TestClass`<T`>::testMethod(T b,std::map<T,int> m){ m[b]=0; } #endif /*TESTCLASS_H_*/ int main(int argc, char* argv[]) { SomeClass s; TestClass<SomeClass> t; map<SomeClass,int> m; t.testMethod(s,m); } Compiler gives me following error in line m[b]=0; : instantiated from 'void TestClass::testMethod(T, std::map) [with T = SomeClass] Could you help find the problem?? Thanks in advance

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• C++ Design Question on template types

  - by user231536

  I have a templated class template <typename T> class MyContainerClass For types to be substituted for T, it has to satisfy many requirements: for example, get_id(), int data(), etc. Obviously none of the fundamental types (PODs) are substitutable. One way I can provide this is via wrappers for the PODs that provide these functions. Is this an acceptable way? Another way would be to change the template to: template < typename T, typename C=traits<T> > class MyContainerClass and inside MyContainerClass, call traits::data() instead of data() on T objects. I will specialize traits<int>, traits<const char *> etc. Is this good design ? How do I design such a traits class (completely static methods or allow for inheritance) ? Or are the wrapper classes a good solution? What other alternatives are there?

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• Why use shorter VARCHAR(n) fields?

  - by chryss

  It is frequently advised to choose database field sizes to be as narrow as possible. I am wondering to what degree this applies to SQL Server 2005 VARCHAR columns: Storing 10-letter English words in a VARCHAR(255) field will not take up more storage than in a VARCHAR(10) field. Are there other reasons to restrict the size of VARCHAR fields to stick as closely as possible to the size of the data? I'm thinking of Performance: Is there an advantage to using a smaller n when selecting, filtering and sorting on the data? Memory, including on the application side (C++)? Style/validation: How important do you consider restricting colunm size to force non-sensical data imports to fail (such as 200-character surnames)? Anything else? Background: I help data integrators with the design of data flows into a database-backed system. They have to use an API that restricts their choice of data types. For character data, only VARCHAR(n) with n <= 255 is available; CHAR, NCHAR, NVARCHAR and TEXT are not. We're trying to lay down some "good practices" rules, and the question has come up if there is a real detriment to using VARCHAR(255) even for data where real maximum sizes will never exceed 30 bytes or so. Typical data volumes for one table are 1-10 Mio records with up to 150 attributes. Query performance (SELECT, with frequently extensive WHERE clauses) and application-side retrieval performance are paramount.

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• MySQL updating a field to result of a function

  - by jdborg

  mysql> CREATE FUNCTION test () -> RETURNS CHAR(16) -> NOT DETERMINISTIC -> BEGIN -> RETURN 'IWantThisText'; -> END$$ Query OK, 0 rows affected (0.00 sec) mysql> SELECT test(); +------------------+ | test() | +------------------+ | IWantThisText | +------------------+ 1 row in set (0.00 sec) mysql> UPDATE `table` -> SET field = test() -> WHERE id = 1 Query OK, 1 row affected, 1 warning (0.01 sec) Rows matched: 1 Changed: 1 Warnings: 1 mysql> SHOW WARNINGS; +---------+------+----------------------------------------------------------------+ | Level | Code | Message | +---------+------+----------------------------------------------------------------+ | Warning | 1265 | Data truncated for column 'test' at row 1 | +---------+------+----------------------------------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT field FROM table WHERE id = 1; +------------------+ | field | +------------------+ | NULL | +------------------+ 1 row in set (0.00 sec) What I am doing wrong? I just want field to be set to the returned value of test() Forgot to mention field is VARCHR(255)

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• Simple C++ code (what's wrong here?)

  - by JW

  Noob to C++. I'm trying to get user input (Last Name, First Name Middle Name), change part of it (Middle Name to Middle Initial) and then rearrange it (First Middle Initial Last). Where am I messing up in my code? --Thanks for ANY help you can offer! ... #include <iostream> using std::cout; using std::cin; #include <string> using std::string; int main() { string myString, last, first, middle; cout << "Enter your name: Last, First Middle"; cin >> last >> first >> middle; char comma, space1, space2; comma = myString.find_first_of(','); space1 = myString.find_first_of(' '); space2 = myString.find_last_of(' '); last = myString.substr (0, comma); // user input last name first = myString.substr (space1+1, -1); // user input first name middle = myString.substr (space2+1, -1); // user input middle name middle.insert (0, space2+1); // inserts middle initial in front of middle name middle.erase (1, -1); // deletes full middle name, leaving only middle initial myString = first + ' ' + middle + ' ' + last; // return 0; }

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• Java/Python: Integration, problem with looping updating text

  - by Jivings

  Hello! Basically I have a script in Python that grabs the text from an open window using getWindowText() and outputs it to the screen. The python loops so as the text in the window changes, it outputs the changes, so the output of the python will always be up to date with the window text. I'm trying to access this text in my Java program by executing the python script as a process and reading the text it outputs using a buffered reader. For some reason this works fine for the first block of text, but will not read any more after this, it wont read any updates to the text as the python outputs it. Can someone shed some light on this? I'm about to try and use Jython, but I'd really like to know what the problem is here... try { Runtime r = Runtime.getRuntime(); Process p = r.exec("cmd /c getText.py"); BufferedReader br = new BufferedReader( new InputStreamReader(p.getInputStream())); int line; while (true) { line = br.read(); System.out.print((char) line); } } catch (Exception e) { e.printStackTrace(); }

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• "for" loop from program 7.6 from Kochan's "Programming in Objective-C"

  - by Mr_Vlasov

  "The sigma notation is shorthand for a summation. Its use here means to add the values of 1/2^i, where i varies from 1 to n. That is, add 1/2 + 1/4 + 1/8 .... If you make the value of n large enough, the sum of this series should approach 1. Let’s experiment with different values for n to see how close we get." #import "Fraction.h" int main (int argc, char *argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; Fraction *aFraction = [[Fraction alloc] init]; Fraction *sum = [[Fraction alloc] init], *sum2; int i, n, pow2; [sum setTo: 0 over: 1]; // set 1st fraction to 0 NSLog (@"Enter your value for n:"); scanf ("%i", &n); pow2 = 2; for (i = 1; i <= n; ++i) { [aFraction setTo: 1 over: pow2]; sum2 = [sum add: aFraction]; [sum release]; // release previous sum sum = sum2; pow2 *= 2; } NSLog (@"After %i iterations, the sum is %g", n, [sum convertToNum]); [aFraction release]; [sum release]; [pool drain]; return 0; } Question: Why do we have to create additional variable sum2 that we are using in the "for" loop? Why do we need "release previous sum" here and then again give it a value that we just released? : sum2 = [sum add: aFraction]; [sum release]; // release previous sum sum = sum2; Is it just for the sake of avoiding memory leakage? (method "add" initializes a variable that is stored in sum2)

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• replacing elements horizontally and vertically in a 2D array

  - by wello horld

  the code below ask for the user's input for the 2D array size and prints out something like this: (say an 18x6 grid) .................. .................. .................. .................. .................. .................. code starts here: #include <stdio.h> #define MAX 10 int main() { char grid[MAX][MAX]; int i,j,row,col; printf("Please enter your grid size: "); scanf("%d %d", &row, &col); for (i = 0; i < row; i++) { for (j = 0; j < col; j++) { grid[i][j] = '.'; printf("%c ", grid[i][j]); } printf("\n"); } return 0; } I now ask the user for a string, then ask them where to put it for example: Please enter grid size: 18 6 Please enter word: Hello Please enter location: 0 0 Output: Hello............. .................. .................. .................. .................. .................. Please enter location: 3 4 Output: .................. .................. .................. ..Hello........... .................. .................. program just keeps going. Any thoughts on how to modify the code for this? PS: Vertical seems way hard, but I want to start on horizontal first to have something to work on.

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• Deleting first and last element of a linked list in C

  - by LuckySlevin

  struct person { int age; char name[100]; struct person *next; }; void delfirst(struct person **p)// For deleting the beginning { struct person *tmp,*m; m = (*p); tmp = (*p)->next; free(m); return; } void delend(struct person **p)// For deleting the end { struct person *tmp,*m; tmp=*p; while(tmp->next!=NULL) { tmp=tmp->next; } m->next=tmp; free(tmp); m->next = NULL; return; } I'm looking for two seperate functions to delete the first and last elements of a linked list. Here is what i tried. What do you suggest? Especially deleting first is so problematic for me.

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• C++: Maybe you know this pitfall?

  - by Martijn Courteaux

  Hi, I'm developing a game. I have a header GameSystem (just methods like the game loop, no class) with two variables: int mouseX and int mouseY. These are updated in my game loop. Now I want to access them from Game.cpp file (a class built by a header-file and the source-file). So, I #include "GameSystem.h" in Game.h. After doing this I get a lot of compile errors. When I remove the include he says of course: Game.cpp:33: error: ‘mouseX’ was not declared in this scope Game.cpp:34: error: ‘mouseY’ was not declared in this scope Where I want to access mouseX and mouseY. All my .h files have Header Guards, generated by Eclipse. I'm using SDL and if I remove the lines that wants to access the variables, everything compiles and run perfectly (*). I hope you can help me... This is the error-log when I #include "GameSystem.h" (All the code he is refering to works, like explained by the (*)): In file included from ../trunk/source/domein/Game.h:14, from ../trunk/source/domein/Game.cpp:8: ../trunk/source/domein/GameSystem.h:30: error: expected constructor, destructor, or type conversion before ‘*’ token ../trunk/source/domein/GameSystem.h:46: error: variable or field ‘InitGame’ declared void ../trunk/source/domein/GameSystem.h:46: error: ‘Game’ was not declared in this scope ../trunk/source/domein/GameSystem.h:46: error: ‘g’ was not declared in this scope ../trunk/source/domein/GameSystem.h:46: error: expected primary-expression before ‘char’ ../trunk/source/domein/GameSystem.h:46: error: expected primary-expression before ‘bool’ ../trunk/source/domein/FPS.h:46: warning: ‘void FPS_SleepMilliseconds(int)’ defined but not used This is the code which try to access the two variables: SDL_Rect pointer; pointer.x = mouseX; pointer.y = mouseY; pointer.w = 3; pointer.h = 3; SDL_FillRect(buffer, &pointer, 0xFF0000);

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• Building argv and argc

  - by Wylie Coyote SG.

  I'm a student programmer using Qt to build a GUI application for work. The primary purpose of this application is to open some of our old style files, allows better editing and then save the file in a new format and file extension. Recently I have been asked to allow this conversion to take place from a terminal. While I do know what argv and argc are along with what they represent I am unsure how to accomplish what they want. For instance how to handle relative paths vs. absolute... maybe how to get absolute from relative; perhaps none of that is even needed. My programming experience has been primarily with guis so this is a little new to me. Users would like the following to be ran from the terminal application -o /fileLocation /fileDestination template(to determine new format) I began to use for loops and if statements to begin accomplishing this when I relized that I might be taking the worng approach to all of this. I WOULD ALSO BE REALLY INTERESTED IF QT HAS SOMETHING FOR THIS! Here is what I have began coming up with: int main(int argc, char *argv[]) { if(argc > 1) { for(int i = 0; i < argc; i++) { if(argv[i] == "-c") { QString fileName = QString::fromStdString(argv[i+1]); QString fileDestination = QString::fromStdString(argv[i+2]); QString templateName = QString::fromStdString(argv[i+3]); QFile fileToConvert(fileName); if(fileToConvert.open(QFile::ReadOnly)) { //do stuff Thanks for reading my post and a big thanks for any contributions you make to helping me overcome this issue.

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• C macro issue: redefinition of functions / structure

  - by Andrei Ciobanu

  Given the following code (it's a macro that generates code for a list data structure, based on the contained type). list.h #ifndef _LIST_H #define _LIST_H #ifdef __cplusplus extern "C" { #endif #define LIST_TEMPLATE_INIT(type) \ typedef struct __list_s_##type { \ struct __list_s_##type *next; \ type value; \ } __list_##type; \ \ __list_##type * __list_##type##_malloc(type value){ \ __list_##type * list = NULL; \ list = malloc(sizeof(*list)); \ list->value = value; \ return list; \ }\ \ void __list_##type##_free(__list_##type *list){\ __list_##type * back = list;\ while(list=list->next){\ free(back);\ back = list;\ }\ } #define LIST_TYPE(type) __list_##type #define LIST_MALLOC(type,value) __list_##type##_malloc(value) #define LIST_FREE(type,list) __list_##type##_free(list) #define LIST_DATA(list) (list->value) #ifdef __cplusplus } #endif #endif /* _LIST_H */ And here is how the above code works: #include <stdio.h> #include <stdlib.h> #include "list.h" /* * */ LIST_TEMPLATE_INIT(int) int main(int argc, char** argv) { LIST_TYPE(int)* list = NULL; list = LIST_MALLOC(int, 5); printf("%d",LIST_DATA(list)); LIST_FREE(int,list); return (0); } My question, is it possible to somehow be able to call : LIST_TEMPLATE_INIT(int), as many times as I want, in a decentralized fashion ? The current issue with this right now is that calling LIST_TEMPLATE_INIT(int) in another file raise compilation errors (because of function redefinition): Example of error: error: redefinition of ‘struct __list_s_int’

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• How to negate a predicate function using operator ! in C++?

  - by Chan

  Hi, I want to erase all the elements that do not satisfy a criterion. For example: delete all the characters in a string that are not digit. My solution using boost::is_digit worked well. struct my_is_digit { bool operator()( char c ) const { return c >= '0' && c <= '9'; } }; int main() { string s( "1a2b3c4d" ); s.erase( remove_if( s.begin(), s.end(), !boost::is_digit() ), s.end() ); s.erase( remove_if( s.begin(), s.end(), !my_is_digit() ), s.end() ); cout << s << endl; return 0; } Then I tried my own version, the compiler complained :( error C2675: unary '!' : 'my_is_digit' does not define this operator or a conversion to a type acceptable to the predefined operator I could use not1() adapter, however I still think the operator ! is more meaningful in my current context. How could I implement such a ! like boost::is_digit() ? Any idea? Thanks, Chan Nguyen

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• stdio data from write not making it into a file

  - by user1551209

  I'm having a problem with using stdio commands for manipulating data in a file. I short, when I write data into a file, write returns an int indicating that it was successful, but when I read it back out I only get the old data. Here's a stripped down version of the code: fd = open(filename,O_RDWR|O_APPEND); struct dE *cDE = malloc(sizeof(struct dE)); //Read present data printf("\nreading values at %d\n",off); printf("SeekStatus <%d>\n",lseek(fd,off,SEEK_SET)); printf("ReadStatus <%d>\n",read(fd,cDE,deSize)); printf("current Key/Data <%d/%s>\n",cDE->key,cDE->data); printf("\nwriting new values\n"); //Change the values locally cDE->key = //something new cDE->data = //something new //Write them back printf("SeekStatus <%d>\n",lseek(fd,off,SEEK_SET)); printf("WriteStatus <%d>\n",write(fd,cDE,deSize)); //Re-read to make sure that it got written back printf("\nre-reading values at %d\n",off); printf("SeekStatus <%d>\n",lseek(fd,off,SEEK_SET)); printf("ReadStatus <%d>\n",read(fd,cDE,deSize)); printf("current Key/Data <%d/%s>\n",cDE->key,cDE->data); Furthermore, here's the dE struct in case you're wondering: struct dE { int key; char data[DataSize]; }; This prints: reading values at 1072 SeekStatus <1072> ReadStatus <32> current Key/Data <27/old> writing new values SeekStatus <1072> WriteStatus <32> re-reading values at 1072 SeekStatus <1072> ReadStatus <32> current Key/Data <27/old>

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• iPhone AES encryption issue

  - by Dilshan

  Hi, I use following code to encrypt using AES. - (NSData*)AES256EncryptWithKey:(NSString*)key theMsg:(NSData *)myMessage { // 'key' should be 32 bytes for AES256, will be null-padded otherwise char keyPtr[kCCKeySizeAES256 + 1]; // room for terminator (unused) bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding) // fetch key data [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding]; NSUInteger dataLength = [myMessage length]; //See the doc: For block ciphers, the output size will always be less than or //equal to the input size plus the size of one block. //That's why we need to add the size of one block here size_t bufferSize = dataLength + kCCBlockSizeAES128; void* buffer = malloc(bufferSize); size_t numBytesEncrypted = 0; CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding, keyPtr, kCCKeySizeAES256, NULL /* initialization vector (optional) */, [myMessage bytes], dataLength, /* input */ buffer, bufferSize, /* output */ &numBytesEncrypted); if (cryptStatus == kCCSuccess) { //the returned NSData takes ownership of the buffer and will free it on deallocation return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted]; } free(buffer); //free the buffer; return nil; } However the following code chunk returns null if I tried to print the encryptmessage variable. Same thing applies to decryption as well. What am I doing wrong here? NSData *encrData = [self AES256EncryptWithKey:theKey theMsg:myMessage]; NSString *encryptmessage = [[NSString alloc] initWithData:encrData encoding:NSUTF8StringEncoding]; Thank you

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• String Index Out Of Bound Exception error

  - by Fd Fehfhd

  Im not really sure why a am getting this error. But here is my code it is meant to test palindromes disregarding punctuation. So here is my code import java.util.Scanner; public class PalindromeTester { public static void main(String [] args) { Scanner kb = new Scanner(System.in); String txt = ""; int left; int right; int cntr = 0; do { System.out.println("Enter a word, phrase, or sentence (blank line to stop):"); txt = kb.nextLine(); txt = txt.toLowerCase(); char yP; String noP = ""; for (int i = 0; i < txt.length(); i++) { yP = txt.charAt(i); if (Character.isLetterOrDigit(txt.charAt(yP))) { noP += yP; } } txt = noP; left = 0; right = txt.length() -1; while (txt.charAt(left) == txt.charAt(right) && right > left) { left++; right--; } if (left > right) { System.out.println("Palindrome"); cntr++; } else { System.out.println("Not a palindrome"); } } while (!txt.equals("")); System.out.println("You found " + cntr + " palindromes. Thank you for using palindromeTester."); } } And if i test it and then i put enter so it will tell me how many palindromes you found the error i am getting is javav.lang.StringIndexOutOfBoundException : String index out of range 0 at PalindromeTester.main(PalindromeTester.java:38) and line 28 is while (txt.charAt(left) == txt.charAt(right) && right > left) Thanks for the help in advance

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